topic 8 acids and alkalis

Question 1

what do these hazard symbols mean?

Answer 1

Question 2

what ion is present in all acids?

Answer 2

H⁺

Question 3

what ion is present in all alkalis?

Answer 3

OH^-

Question 4

what pH is acidic?

Answer 4

below 7

Question 5

what pH is neutral?

Answer 5

7

Question 6

what pH is alkali?

Answer 6

above 7 and below 14

Question 7

what does acidic, neutral and alkaline look like on these common indicators?

litmus paper

methyl orange

phenolphthalein

Answer 7

acidic neutral alkaline

litmus paper red purple blue

methyl orange red yellow yellow

phenolphthalein colourless colourless pink

Question 8

what is the link between pH and the concentration of ions?

Answer 8

a very low pH means that there are lots of H⁺ ions e.g. HCL, in which half of the acid consists of H⁺ ions.

a pH of 7 means there are no H⁺ or OH^- ions

a very high pH means there are a lot of OH^- ions in the alkali

Question 9

what does stron/weak mean in terms of acids and alkalis?

Answer 9

a strong acid/alkali has a lot of H⁺/OH^- ions present in the chemical, the molecules fully dissociate

weak means there are not many of these ions present in the chemical, the molecules dont fully dissociate

Question 10

what does dilute/concentrated mean in terms of solute in a soltion?

Answer 10

a dilute solution means that there is not much solute for every bit of solvent and concentrated means there is a lot of solute for every bit of solvent

Question 11

describe how a base reacts in a neutralisation reaction

Answer 11

bases, which consist of a + metal ion and an O^2- ion, cancles out the charge of the H⁺ions by making water(2H⁺+O² > H₂O) and the metal ion reacts with the nonmetal ion in the acid to form a salt

Question 12

what are the steps in preparing a soluble salt from an acid and an insoluble salt

Answer 12

hav the acid in a beaker and keep adding and sturing in the insoluble reactant untill there is exess on the top which wont react, filter the solution to remove the exess reactant, evapourate off the water from the solution, you have salt

Question 13

why do you use an exess of insoluble reactant when preparing a soluble salt?

Answer 13

when all of the acid has reacted, you will have a solution of salt dissolved in water. the insoluble salt cannot reaqct with the solution and wont dissolve, so can be easily filtered out to leave just the solution of water and salt

Question 14

what is the difference between an alkali and a base?

Answer 14

an alkali is a soluble base

/a base is an insoluble alkali

Question 15

acid + alkali >?

Answer 15

water + salt

Question 16

acid + metal > ?

Answer 16

salt + hydrogen

Question 17

acid + carbonate > ?

Answer 17

salt + water + carbon dioxide

Question 18

acid + base > ?

Answer 18

salt + water

Question 19

why is titration used to prepare a soluble salt from an acid and an alkali?

Answer 19

because it is very accurate and you end up with alot less exess acid or alkali left over in the final solution

Question 20

how do you carry out an acid-alkali titration

Answer 20

using a pipette filler and a graduated glasspipette, measure out a known amount(say 100ml) of the acid and put it into a conical flask. Then fill the buret with the alkali, slowly add the alkali to the conical flask untill the solution is nutral. you can redo this many times to get a more accurate measurment.

Question 21

what is the test for hydrogen gas?

Answer 21

lit splint, goes po

Question 22

the test for carbon dioxide?

Answer 22

bubble it through lime water, it should go cloudy and white

Question 23

what are the rules of solubility?

Answer 23

all common sodium, potassium and ammonium salts are soluble

all nitrates are soluble

most chlorides are soluble, except silver and lead

most sulphates are soluble, except lead, barium and calcium

most carbonated and hydroxides are insoluble, except sodium, potassium and ammonium

Question 25

What is a precipitation reaction?

Answer 25

When 2 solution( in this case a salt dissolved in water) react to form an insoluble salt

Question 26

What is the precipitate?

Answer 26

The precipitate is the insoluble salt formed from a precipitation reaction